1. The problem statement, all variables and given/known data A solution of histidine has all acid-base groups protonated. The pKa of the carboxy group is 1.8, the amino group is 9.2, and the side chain is 6.0. For each mole of amino acid, 2.5 moles of NaOH are added. What is the pH of the solution? 2. Relevant equations Henderson-Hasselbalch equation: pH = pKa + log ([A-]/[HA]) 3. The attempt at a solution I am trying to answer this question for a practice exam. I know that the base will deprotonate the protein, starting from the carboxy group followed by the side chain. I assume that the NaOH is very basic, so it will definitely cause a pH of greater than 6.0. How do I proceed from there? My attempt: pH = unknown pKa = 1.8, 6.0, 9.2 [A-]/[HA] = 2.5 pH = 9.2 + log(2.5) = 9.59, but this is wrong. Could someone please help me with this problem. Thank you very much.